Iron particles for purifying contaminated soil or ground water

Abstract

Iron particles for purifying soil or ground water of the present invention comprise a mixed phase of α-Fe phase and Fe3O4 phase, and having a BET specific surface area of 5 to 60 m2 / g, an Fe content of not less than 75% by weight based on the weight of the iron particles and a sulfur content of not less than 1,000 ppm. The iron particles are capable of decomposing or insolubilizing harmful substances such as organohalogen compounds and / or heavy metals, cyanogen, etc. contained in the soil or ground water in efficient, continuous and economical manners.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates to iron particles for purifying a contaminated soil or ground water, a process for producing the iron particles, a purifying agent comprising the iron particles, a process for producing the purifying agent, and a method of purifying the contaminated soil or ground water. More particularly, the present invention relates to iron particles for purifying a soil or ground water contaminated with harmful substances such as organohalogen compounds, heavy metals, cyanogens and / or agricultural chemicals, which are capable of decomposing or insolibilizing the harmful substances contained in the soil or ground water, e.g., aliphatic organohalogen compounds such as dichloromethane, carbon tetrachloride, 1,2-dichloroethane, 1,1-dichloroethane, cis-1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane, trichloroethylene, tetrachloroethylene and 1,3-dichloropropene, aromatic organohalogen compounds such as dioxins and PCB ...

AI Technical Summary

Benefits of technology

[0048] It is an object of the present invention to provide iron particles for purifying a contaminated soil or ground water, which are capable of decomposing or insolubilizing harmful substances such as organohalogen compounds and / or heavy metals, cyanogen, etc. contained in the soil or ground water in efficient, continuous and economical manners.

[0049] It is another object of the present invention to provide a purifying agent for a contaminated soil or ground water, which is capable of decomposing or insolubilizing harmful substances such as organohalogen compounds and / or heavy metals, cyanogen, etc. contained in the soil or ground water in efficient, continuous and economical manners.

Problems solved by technology

Also, waste gases, fly ashes or main ashes discharged from an incineration furnace for combusting municipal garbage or industrial wastes, contain dioxins as aromatic organohalogen compounds having an extremely high toxicity to human bodies though the amount thereof is trace.

Since the PCB is very harmful, the production and use thereof has been presently prohibited.

However, any effective method of treating PCB past used has not been established until now and, therefore, a large part thereof has still been stored without treatment or disposal.

The above-described aliphatic organohalogen compounds and aromatic organohalogen compounds are hardly decomposable, and further exhibit carcinogenesis as well as a strong toxicity.

Therefore, there arises such a significant environmental pollution that soil or ground water is contaminated with these organohalogen compounds.

More specifically, upon discharge of such organohalogen compounds, the aromatic organohalogen compounds such as dioxins and PCB which are hardly decomposable and exhibit a strong toxicity, cause significant environmental problems such as contamination of soil and ground water.

In the case where such hardly-decomposable aromatic halogen compounds are accumulated in soil, the soil is contaminated therewith and as a result, the contaminated soil then cause contamination of ground water by the organohalogen compounds.

Further, the contaminated ground water runs out from the contaminated soil to surrounding regions, so that pollution by the organohalogen compounds expands over much wider areas.

The land in which soil is once contaminated with the organohalogen compounds, cannot be reused and developed again.

However, since the organohalogen compounds are hardly decomposable and a large amount of soil and ground water must be purified, any efficient and economical purifying techniques or methods cannot be fully established until now.

Alternatively, the contamination of soil or ground water by another harmful substances including heavy metals such as cadmium, lead, chromium (VI) and arsenic as well as cyanogen, etc., adversely affects human bodies and ecosystem.

However, since detailed properties and specific amount of the iron particles used are not described, it is considered that this method fails to fully reduce the organohalogen compounds.

However, since the raw material used in this method is derived from iron ore, it is presumed that a large amount of impurities contained in most of common steel components or common cast iron components are involved therein.

Therefore, the iron particles may fail to show a high purification property against the organohalogen compounds.

In addition, although the specific surface area and particle size of the iron particles are described, since the particle size thereof is too large, it may be difficult to fully reduce the aromatic organohalogen compounds.

However, in Examples of this KOKAI, it is essentially required to heat the kneaded material at a temperature of not less than 250° C. Therefore, this method may fail to provide an economical process.

Therefore, the iron particles may fail to show a high purification property against the organohalogen compounds.

Further, since decomposition of the organohalogen compounds requires a long period of time, this method may fail to efficiently convert the organohalogen compounds into harmless ones.

However, since this method essentially requires to use amines for accelerating the dehalogenation reaction, it is difficult to fully conduct the decomposition reaction by the reducing metal.

However, since the iron-based metals are in the form of fibers having a large fiber diameter, this method may also fail to fully reduce the aromatic organohalogen compounds.

Therefore, the mill scale may fail to show a high purification property against the organohalogen compounds.

Also, in order to promote conversion of the organohalogen compounds into harmless ones, since the use of the aqueous hydrochloric acid solution is essentially required, the mill scale by itself may fail to sufficiently promote the decomposition reaction.

However, since the iron particles used have a too large particle size, it may be difficult to fully decompose the organohalogen compounds.

However, in order to promote the conversion of dioxins into harmless ones, since the use of the aqueous hydrochloric acid solution is essentially required, the iron compound by itself may fail to sufficiently promote the decomposition reaction.

Therefore, the spherical iron particles may fail to show a high purification property against the organohalogen compounds.

Further, since the water suspension containing the spherical iron particles obtained by collecting dusts contained in waste gas discharged during refining process from an oxygen-blowing converter for steel-making and removing gases from the dusts, the iron particles have a broad particle size distribution and, therefore, exhibit a non-uniform penetration velocity into contaminated soil, resulting in delayed purification performance and prolonged purification time.

For this reason, the water suspension may also fail to fully reduce the organohalogen compounds.

In addition, although spherical iron particles having an average particle diameter of 1.3 μm were used in Examples of this KOKAI, since the metal iron content thereof is low, it may be difficult to fully reduce the organohalogen compounds.

For this reason, since it is presumed that the iron particles usually contain a large amount of impurities derived from the mill scale or molten steel, the iron particles may fail to show a high purification property against the organohalogen compounds.

Thus, the iron particles may also fail to fully reduce the organohalogen compounds.

On the other hand, the other harmful substances contained in contaminated soil or ground water including heavy metals such as cadmium, lead, chromium (VI) and arsenic as well as cyanogen, agricultural chemicals or the like, are similarly harmful to human bodies and ecosystem.

However, the above conventional treatment techniques undergo high treating costs, and require a long treating time.

Therefore, these techniques may fail to reduce harmful substances such as heavy metals, cyanogen, agricultural chemicals, etc., in efficient and continuous manners.

Therefore, with the passage of years, there arise problems such as deterioration in persistency of reducing activity of the iron particles.

As a result, there is such a tendency that the heavy metals converted into harmless and stabilized ones having a low valence, are converted again into harmful metals having an increased valence.

Thus, the above techniques may fail to provide a method or measure that is effectively usable for a long period of time.

Also, it is described that when the pH value is low, elution of the iron particles is increased, resulting in deterioration in the adsorption / removal effect thereof.

However, this technique essentially requires pH adjustment by addition of alkali as well as heating and forced oxidation.

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